1. Field of the Invention
The present invention relates to a fuel control for an internal combustion engine.
2. Description of the Related Art
In a technique disclosed in Japanese Patent Publication Laid-Open (JP-A) No. 6-159182, a cylinder internal pressure is detected to determine a cylinder internal pressure maximum pressure Pmax, a rate of pressure change dP/dθ, and a compression ignition timing. Stability of compression ignition timing is determined from these values, and a pilot fuel amount is controlled according to the determination result.
In a technique disclosed in JP-A No. 2005-147025, an actual torque is computed according to the detected cylinder internal pressure. A correction amount is computed based on a required torque and the actual torque using a sequential statistical algorithm. A fuel injection amount is corrected according to the correction amount.
In an internal combustion engine such as a Diesel engine, the fuel injection is divided into pilot injection and main injection to sluggishly perform combustion, thereby avoiding deterioration of a combustion noise caused by the rapid combustion.
On the other hand, the combustion of the internal combustion engine may be largely fluctuated by a cetane number, humidity, deterioration of a fuel injection valve, and a variation in the compression ratio among cylinders. Therefore, a variation in an actual rate of heat release may occur in the internal combustion engine, even if the fuel injection is performed according to an injection timing and an injection amount based on a map (table) that is previously set and stored in a control apparatus.
In order to address the variation in the rate of heat release, it has been proposed that a compression ignition position of the combustion is detected with a sensor for detecting the cylinder internal pressure and/or a sensor for detecting knocking, and a feedback control is performed for the main injection.
However, even if the feedback control is performed for the main injection, deterioration of the combustion noise and/or emission may occur when the combustion by the pilot injection is lowered or excessive.
Accordingly there is a demand for a technique of being capable of avoiding such deterioration that may be caused by the combustion by the pilot injection.